Metallated rosin inks for gravure printing commonly contain ethyl cellulose or ethyl hydroxyethyl cellulose as a thickener. However, the prices of ethyl cellulose and of other cellulose derivatives has escalated to an extent that a substitute (partial or complete) is needed. As is known, limed rosin has long been used in similar inks as is noted in U.S. Pat. No. 3,409,449, which gives suitable dyes and pigments for use in such inks.
U.S. Pat. No. 2,886,549 is concerned with aliphatic hydrocarbon (benzine) soluble acrylic polymers for use as lacquers, inks, and textile impregnants. The polymer is solution polymerized at 90.degree. C. and 120.degree. C. which would give a low molecular weight polymer, and molecular weight (not specified) can be controlled with conventional polymerization regulators. The polymers have at least two components, with a third optional component. The first component (50-90 parts) is a cycloalkyl ester of an unsaturated acid such as acrylic acid, methacrylic acid or fumaric acid, etc; the preferred alcohol moiety is, for example, cyclohexanol, mono-, di, or trimethyl cyclohexanol, or other substituted cyclohexanol. The second component (10-50 parts) is an ester of (meth)acrylic acid with an alcohol of at least eight carbon atoms, preferably 10-18 carbons. The third and optional component (1-20 parts) is a different polymerizable compound such as vinyl acetate, styrene, etc., or one having a reactive aldehyde, epoxy, carboxy, etc. group. Of the examples, Examples 1 (80 cyclohexyl methacrylate (CHMA), 20 dodecyl methacrylate (DMA)) gives a polymer with the highest calculated Tg of the examples--just below 30.degree. C. At 90 CHMA and 10 DMA, the calculated (not actual) Tg would be about 45.degree. C. As elsewhere herein, unless specified otherwise, the Tg is the calculated value using the method of Fox (infra). At 50 CHMA and 50 DMA, this value would be -15.degree. C. Being solution polymerized at high temperatures, the polymer would have a quite low molecular weight.
A similar disclosure of alkane (ligroine or benzine) soluble acrylic polymers appears in British patent No. 772,746, which, based on CA. 51, 10925f, involves a copolymer of 20-40% of a higher alkyl ester such as dodecyl methacrylate or cyclohexyl methacrylate, with styrene and the like. An example is given of a polymer in parts by weight of 680 styrene, 320 dodecyl methacrylate, and 200 methyl methacrylate. This would have a calculated Tg of about 36.degree. C. and, because of the polymerization method, a very low molecular weight. If it is assumed the polymer is 20 CHMA and 80 styrene, the calculated Tg is about 90.degree. C. whereas with 20 DMA and 80 St the figure is about 50.degree. C. The polymer may be combined with other coating materials such as drying oils, phthalic acid resins, etc.
A condensation polymer, of a copolymer of acrylic acid-butyl methacrylate-methyl methacrylate with rosin modified by glycerol, fumaric acid and pentarythritol, for use as an additive in rosin inks, is the subject of Japanese patent publication No. 73/18,332 June 5, 1973. This is reported in Chemical Abstracts 80:97528r.
Experimental use has also been made of solution-polymerized polymers of 97% isobutyl methacrylate and 3% of a methacrylate; these were not wholly satisfactory, because solution-polymerized polymers inherently have low molecular weights, and are comparatively inefficient thickeners.
CA 84:46321T discloses a gravure ink of a low T.sub.g alkane soluble acrylic resin and an alkane insoluble acrylic resin.
Another reference of possible interest is U.S. Pat. No. 2,803,611, concerned with an adhesive which contains a blend of a copolymer of lauryl and hexyl methacrylates with limed rosin, a wax-naphthalene condensate and a solvent, particularly a hydrocarbon solvent. These higher methacrylic acid esters give very soft (T.sub.g &lt;-5.degree. C.) polymers which normally cannot be produced as a powder. In addition, they have a plasticizing effect upon the hard binder and are not shown by the reference to have any effect in thickening the composition, particularly so in view of the fact that clay is included in the composition to give thickening.
A U.S. patent application related to the present application is that of Swift et al, Ser. No. 766,391, filed Feb. 7, 1977; it concerns lithographic inks in which the binder is a copolymer, having a Mn of 1,000 to 15,000, of up to 40% isobornyl methacrylates (iBOMA) with, for example, isobutyl methacrylate and an unsaturated acid. The ink contains an aliphatic hydrocarbon solvent.
Another patent concerned with isobornyl methacrylate is U.S. Pat. No. 3,485,775. It discloses polymers containing 25-75% isobornyl methacrylate and substantial amounts of methyl methacrylate mers, which detract from hydrocarbon solubility of the polymer. Small amounts of styrene, ethyl acrylate, or butyl acrylate are permitted. The disclosed molecular weight range of the polymers of this reference is between 10,000 to 2,000,000. No unsaturated acid monomers are suggested.
U.S. Pat. No. 3,681,298 discloses polymers having a molecular weight range of 1,000 to 8,500, containing 40-60% isobornyl methacrylate and 40-60% of methyl methacrylate, styrene, s-butyl methacrylate, or o-butyl methacrylate, and up to 5% of an unsaturated acid, and the use of solvents comprising or consisting of paraffins, e.g., octane. Amounts of monomers such as methyl methacrylate for such low molecular weight polymers do not appear to be particularly critical; thus about 50% methyl methacrylate is useful. In the present invention, involving high molecular weight polymers, such quantities of methyl methacrylate would result in insoluble polymers. The pending application Ser. No. 766,391 and the latter two patents are assigned to the assignee of the instant application.
Other acrylic copolymers for inks are also known, as shown for example in U.S. Pat. No. 3,764,587 (Zunker). The inherent viscosity of the polymer of the latter patent, a measure of molecular weight, is between 0.2 and 0.35 measured at 25.degree. C. using 25 milligrams of polymer in 5 cc. of chloroform, which suggest a Mw of 100,000 or greater. The monomers in the polymer are such as would yield in some cases a very rubbery, soft product, having a very low calculated T.sub.g as defined herein. In other cases, depending upon the selection of monomers and ratios, a polymer containing ethyl methacrylate could be obtained which has a calculated T.sub.g of about 40.degree. C. or slightly greater. Ethyl methacrylate, however, as a monomer has a solubility parameter of about 8.3 and a homopolymer thereof has a solubility parameter of about 9.0; the T.sub.g of a homopolymer of ethyl methacrylate being about 65.degree. C., all as shown hereinbelow.
The Aronoff et al polymer (U.S. Pat. No. 3,271,347), in one embodiment is primarily of vinylidene chloride, with acrylic acid, methacrylic acid, or itaconic acid, and with the optional inclusion of other monomers. The vinylidene chloride copolymers have molecular weights in the range of 3,000 to 5,000. Aronoff et al also mention all-acrylic copolymers, the invention being in the inclusion of polyoxethylene ethers in materials such as inks. No method of preparing the acrylic polymer is disclosed nor are molecular weights. The specific acrylics disclosed have extremely low calculated T.sub.g 's. Aronoff et al disclose solvents, including aliphatic hydrocarbons, aromatic hydrocarbons, ketones, alcohols, etc.
Hoshi et al U.S. Pat. No. 3,912,675 concerns flexographic inks containing a filler, 5-35% by weight of an acrylic resin, 5-20% of one or more natural resins selected from copal, dammar and shellac, and a solvent containing at least two of an aromatic hydrocarbon, an alcohol, an ester, and a glycol ether. The acrylic polymer allegedly has a molecular weight of 30,000-300,000, a T.sub.g of 20.degree.-105.degree. C., and may be of isobutyl methacrylate and methacrylic acid (ratios not being given). The intrinsic viscosities given in the examples define polymers which in our experience would have molecular weights no higher than a few hundred. At column 5, lines 35-50, the dynamic viscosities at 25.degree. C. (no solvent specified) are given as 210-400 centipoises for Examples 1-6 and 240-350 centipoises for comparative Examples 1-5. Some of the copolymers are impractical; for our uses in order to get a T.sub.g of &gt;20.degree. with lauryl methacrylate and acrylic acid at least 65% acid would be needed. Such a polymer would not be soluble in aliphatic hydrocarbons, nor would it be compatible with limed rosin.
U.S. Pat. No. 4,005,022 to Vijayendran discloses a liquid toner, for developing electrostatic images, containing (A) 9-99 parts of a saturated aliphatic hydrocarbon having a Kauri-butanol number of 25-35, (B) 1-10 parts of an intensifier. The intensifier (B) contains (1) 1-10 parts soap, 80-97 parts aliphatic hydrocarbon, and (3) 3-20 parts of a concentrate. The concentrate (3) contains (a) 8-14 parts pigment, (b) 120-200 parts of an acrylic or other polymer, (c) 180-240 parts saturated hydrocarbon and (d) 0.03-6 parts pigment. The acrylic polymer "Neocryl B-707" mentioned by Vijayendran ("a terpolymer composed of vinyl toluene, i-butyl methacrylate and lauryl or stearyl methacrylate") appears to be similar to the acid-free isobutyl methacrylate-vinyl toluene copolymers of Brown et al U.S. Pat. No. 3,417,041 (prepared by suspension polymerization using a chain transfer agent to give a low molecular weight). The useful polymers had viscosities in Varsol No. 3 of from 37 to 110 centipoises. Similar waxy polymers made with higher alkyl methacrylates and acids are shown by Finn et al. U.S. Pat. No. 3,532,654 for floor polish emulsions.